Conventional methods such as pick-and-place for applying integrated circuits to a destination substrate are limited to relatively large devices, for example having a dimension of a millimeter or more and it is often difficult to pick up and place ultra-thin, fragile, or small devices using such conventional technologies. More recently, micro-transfer printing methods have been developed that permit the selection and application of such ultra-thin, fragile, or small devices without causing damage to the devices themselves.
Micro-transfer printing enables deterministically removing arrays of micro-scale, high-performance devices from a native source wafer, typically a semiconductor wafer on which the devices are constructed, and assembling and integrating the devices onto non-native destination substrates, such as glass or polymer substrates. In a simple embodiment, micro-transfer printing is analogous to using a rubber stamp to transfer liquid-based inks from an ink-pad onto paper. However, the “inks” are typically composed of high-performance solid-state semiconductor devices and the “paper” can be substrates, including glass, plastics, ceramics, metals, or other semiconductors, for example. An example micro-transfer printing process leverages engineered elastomer stamps coupled with high-precision motion-controlled print-heads to selectively pick up and print large arrays of micro-scale devices from a source native wafer onto non-native destination substrates.
Adhesion between an elastomer transfer device and a printable element can be selectively tuned by varying the speed of the print-head, for example. This rate-dependent adhesion is a consequence of the viscoelastic nature of the elastomer used to construct the transfer device. When the transfer device is moved quickly away from a bonded interface, the adhesion is large enough to “pick” the printable elements away from their native substrates, and conversely, when the transfer device is moved slowly away from a bonded interface the adhesion is low enough to “let go” or “print” the element onto a foreign surface. This process may be performed as a massively parallel operation in which the stamps can transfer, for example, hundreds to thousands of discrete structures in a single pick-up and print operation.
Micro-structured stamps may be used to pick up micro devices from a source substrate, transport the micro devices to the destination, and print the micro devices onto a destination substrate. A transfer device (e.g., micro-structured stamp) can be created using various materials. Posts on the transfer device can be designed to pick up material from a pick-able object and then print the material to the target substrate. The posts can be formed in an array. For effective, high-yield printing, when picking up the material it is important that the stamp posts are in close contact with the material (e.g., micro integrated circuits) being transferred or printed.
In any printing operation, it is important that the destination (receiving) substrate include functional devices at every desired location on the destination substrate at the end of an assembly process and it is therefore important to provide methods and systems for ensuring completely functional micro-transfer-printed structures.